This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. In this project we are investigating the role of protein-protein interactions in the mechanism of metal ion transfers between the key proteins of the bacterial detoxification pathway for inorganic mercury and organomercurials and elucidating the chemical and physical properties embedded in the protein structures that facilitate the directed transfer of Hg(II) to the essential enzyme for reductive detoxification. The structures of four components of the pathway have been determined and the structure of an integral membrane transport protein is being pursued to facilitate structure/function analysis of the proteins. Together with the structural information we use site-directed mutagenesis to evaluate the effects of altered structural features on the individual properties and functions of the several proteins and on their interactions. The goal of the studies is to reveal the features of the proteins that are essential from an evolutionary perspective for this detoxification pathway to be effective. Mass spec has proved invaluable in verifying oxidation and proteolysis problems with several of our mutated enzymes and in verifying formation of metal ion complexes that we have used in our structural and kinetic studies.